With the developments in information communication technologies, bi-directional communication via packet communication networks has been in widespread use. In particular, Internet protocol (IP) telephones that facilitate voice communication via an IP network (e.g., the Internet) have been in widespread use. Such IP telephones employ a voice over Internet protocol (VoIP) in which packetized voice data is transmitted and received via a packet communication network. Accordingly, it is important for service providers that provide an IP telephone service to monitor and manage the quality of voice of an IP telephone.
In order to measure the quality of voice of an IP telephone, a technique of calculating a loss rate of packets per unit time in each of real-time transport protocol (RTP) sessions has been developed. For example, as illustrated in FIG. 33, an amount (referred to as a receipt count of packets) of received packets and an amount (referred to as a loss count of packets) of loss packets per predetermined period of time are counted up, and the loss rate of packets is calculated. Note that in FIG. 33, circles with a solid outline represent received packets, and circles with a dotted outline represent loss packets. In addition, FIG. 33 illustrates a case in which three packets (packets having sequence numbers of 4, 11, and 15) out of one hundred packets have been lost. Thus, the loss rate of packets is 3.0%. Note that it may be determined whether a packet is lost by monitoring the sequence number contained in each of the packets.
Related techniques are disclosed in Japanese Laid-Open Patent Publication No. 2003-249945 and Japanese Laid-Open Patent Publication No. 11-259099.